The TDD2A is a double diode triode for battery receivers. The function was as detector, AGC rectifier and first audio voltage amplifier in a superhet broadcast receiver.
Unlike our other TDD2A's this exhibit has the earlier balloon envelope.
The reverse is unmarked gold coloured zinc paint.
Looking from the top it is possible to see the sections stacked vertically. The triode is at the top as the control grid connects to the top cap.
The balloon envelope is 46 mm in diameter, and excluding the B5 base pins is 109 mm tall.
References: Data-sheet, 1040 & 1043. Type TDD2A was first introduced in 1934. See also1934 adverts.
